The invention relates generally to respiratory insulating masks, and more particularly to a face mask with means for tempering or otherwise conditioning cold air for breathing. Even more particularly, this invention relates to an artificial temporal counter-current heat exchanger.
In the extreme arid cold, typical of the cold deserts of Alaska inside the Arctic Circle and everywhere that animals are exposed to extreme dry cold conditions, man is at a disadvantage. And the inhalation of cold air (-30.degree. C. to -60.degree. C.) can be detrimental to man's health. In an attempt to work and survive in these conditions man has copied the adaptions of the animals living year around in these habitats by increasing his body insulation by putting on various types of cold weather coats, gloves, hats, pants, etc. However, evolution has given all of the animals living in extreme cold an important adaptation that man has not copied. The animals have not only insulated their bodies from the cold but also insulate their respiratory systems to prevent heat and water loss while respiring cold dry air.
All mammals must heat the air they breathe to body temperature (37.degree. C.) and saturate it with water vapor. In temperate climates this does not represent an energy problem for mammals since the ambient temperatures are close to body temperatures and the absolute humidity of the air can be very high. However, in the extreme cold the ability of air to hold water vapor drops to nearly zero and the difference between the temperature of the inhaled air and body temperature is very high. Ambient air temperatures of -30.degree. C. to -60.degree. C. are not uncommon in Alaska and areas in the Arctic where humans live and work. A human breathing -60.degree. C. air must heat every breath nearly 100.degree. C. and add 47 mg of water vapor to every liter of air respired. This costly investment of heat and water is lost by humans when they exhale in the environment. This metabolic cost can be as high as 2-3 times the resting metabolic rate representing a loss of valuable heat and water. This metabolic and water cost raises the energy and water requirements of humans which may otherwise be well insulated against the cold. These energy costs could be critical to humans which are attempting to survive in an emergency situation or exposed during a long-term work effort.
For example, cold adapted species such as reindeer, wolves, seals and polar bears have evolutionary insulated their respiratory systems to prevent heat and water loss. All vertebrate species exposed to cold deserts have evolved some type of temporal counter-current heat exchanger. By vasoconstricting the surface of specialized nasal passages and bones these cold adapted species inhale cold air and cool these surfaces and then exhale over the same surface reducing the temperature of the exhaled air and saving the heat and water that would be lost to the environments, a loss which would have to be replaced in a hostile environment offering little food and water frozen at the temperature of the environment.
In the prior art there are a number of patents which are known to improve the respiratory breathing of humans. For example, U.S. Pat. No. 4,090,513 teaches the humidification of respired air in hospitalized patients; U.S. Pat. No. 4,136,691 teaches a mask for cooling hot air in hot environments wherein the heat exchange portion of the mask is outside the confines of the mask; U.S. Pat. No. 4,325,365 teaches a respiratory mask for cold environments, but exposes the nose to the cold when in use; U.S. Pat. No. 4,196,728 also teaches a respiratory device that exposes the nose to the cold when in use; and, U.S. Pat. No. 4,458,679 teaches a mask utilizing small pipes therein to introduce air into a cavity prior to reception by the wearer. There were a number of respiratory devices which include battery means for heating up the air prior to respiration and these include U.S. Pat. No. 4,601,287; U.S. Pat. No. 4,620,537; U.S. Pat. No. 4,793,343; and U.S. Pat. No. 4,905,686. U.S. Pat. No. 3,814,094 teaches a respiratory mask which includes a counter current exchanger inside the mask which covers substantially the entire inner surface of the mask; and, a great deal of the counter current exchanger inside the mask is insulated from the outside.